Product meter



Aug. 8, 1939.

H. A. THOMPSON PRODUCT METER Filed April 29, 1938 STABILIZED AMPLIFIER.

DEFLECTION INSTRUMENT CU RRENT REGULATOR.

THERMOCOU PL. 5

HEAT; r2

LIGHT BEAM INSTRUMENT.

CURRENT REGULATOR.

SOURCE OF 4 STANDARD VOLTAGE D.Cv

Inventor: Harris AThompson,

- is Attorney.

Patented Aug. 8, 1939 PRODUCT METER Harris A. Thompson,

Schenectady, N. Y.,

signor to General Electric Company, a corporatron "of New York Application April 29, 1938, Serial No. 205,121

3 Claims.

My invention relates to electrical measuring devices and concerns particularly apparatus for measuring a quantity such as power, reactive component of power or some other quantity repre- 5 sentinga product. i

It is an object of my invention to provide a product circuit in which being measured.

Still another object of my invention is to provide a product measuring arrangement which may be used for transmitting indications or records to a distance.

It is furthermore an object of my invention to of operation. 7

Still another object of the invention is to provide an arrangement in which thermocouples.

Other and further objects and advantages will become apparent as the description proceeds.

My invention constitutes an improvement in the wattmeter or product meter described in the copending application of Cramer W. La. Pierre,

Serial No. 205,120, filed concurrently herewith,

Consequently any difference in the relationship between variations in 5 current and variations in current effect of the two adjacent bridge of the apparatus.

arms will not afiect the accuracy In carrying out my invention in its preferred form I multiplied such as voltage and current to two different pairs of diag onally opposite points -or terminals at the corners of the bridge or square so that the two currents to be multiplied flow in the same direction in one thermal-current-responsive arm of the bridge,

and in opposite directions in the other thermal-current-responsive arm of the bridge.

For reasons which will later be explained,

the diiference in heating of the two thermalthe heating, and the auxiliary current is measured. The auxiliary current may be a direct ourmake the arrangem able regulators or 0 photoelectric follow different frequency from any deviation In order to ent automatic I provide suitllow-up arrangements such as -ups for automatically maintaining the auxiliary currents at the proper values.

the drawing, Fig. 1 i a stabilized amplifie hereto. In s a detailed circuit diagram of r forming a part of the appa- Iatus representing one embodiment of my invention. Fig. 2 is a circuit diagram and schematic representation of one embodiment of my invention. Like reference characters are utilized throughout the drawing to designate like parts.

Fig. 2 illustrates an arrangement for measuring the power drawn from an alternating current source 24 by a load 25. There is a four-arm bridge or square 26 having impedance arms I and I2 and two arms in the form of thermal-currentresponsive elements such as thermocouple-heating resistors Hi and M cooperating with thermo couples 2| and 22 respectively. A pair of conductors |5 is connected to diagonally opposite points or terminals l6 and ll of the bridge for supplying a current proportional to, and varying in phase with, current flowing through the load 25. A second pair of conductors I8 is connected to the diagonally opposite points or terminals l9 and 20 of the bridge 26 for supplying to the bridge a current proportional to, and varying in phase with, the voltage between the lines 24 across the load 25. There is a current responsive device 23 to which the thermocouples 2| and 22 are connected in opposition for comparison of their output voltage.

To avoid the necessity for matching the thermocouples 21 and 22 and in order to make the apparatus respond accurately regardless of Whether or not the thermocouples 2| and 22 follow the theoretical square law of thermalcurrent-responsive devices, I provide a current regulator 21 such as a photoelectric follow-up device, for example, for passing an auxiliary current through one of the thermocouple heaters, for example, the heater |3 to equalize the thermocouple temperatures and for indicating the magnitude of the power measured by the apparatus, I provide a current responsive device 28 in series with the output conductors 14 of the current regulator 21.

In order to make it unnecessary for the thermocouples 2| and 22 to follow the same law of relationship between current'in the heater and output voltage, I provide a second current regulator 21a for supplying an additional auxiliary current to the heaters of both thermocouples l3 and I4 of such a magnitude as to maintain the temperatures of the thermocouples 2| and 22 constant regardless of the magnitude of the power being measured by the apparatus. The current regulating systems will be described more in detail hereinafter.

Better results are ordinarily obtained from bridges if the currents supplied across the diagonally opposite terminals are of substantially the same order of magnitude, and furthermore, the power required to operate the bridge 26 may be too great to permit connecting the bridge termmals directly to the load 25. Accordingly, I provide a pair of power amplifiers 33 and 33 with input transformers 29 and 30 and output transformers 31" and 31, respectively, having such ratios of amplification and transformation as to make the currents in the-conductors l8 and I5 substantially equal for the maximum voltage and current of the range for which the apparatus is designed.

The input transformer 29 is a potential transformer having a primary winding connected across the lines of the source 24 and a secondary winding connected to the input side of the amplifier 33', and the input transformer 30 is a current transformer having a primary winding in series with the load 25 and a secondary windin connected to the input side of the amplifier 33. The transformers 3! and 31' have their primary windings connected to the output sides of the amplifiers 33 and 33 and their secondary windings connected to the conductors |5 and i8 respectively.

The current regulator 21 may be a photoelectric follow-up device of v the type described .in Patent No. 1,897,850 La Pierre and in the aforesaid copending application of Cramer W. La Pierre, Serial No. 205,120. Such a photoelectric follow-up system includes a pair of photoelectric cells 4| and 42, means for producing a light beam 62 arranged to be defiect'edback and forth between the photoelectric cells 4|.j'and 42 in response to the polarity and magnitude of current flowing in the current responsive device 23 and means within the regulator 21 (not shown) for causing an output current to flow throughconductors 14 which maintains a constant value when the beam 62 is in a neutral position between the photoelectric cells GI and 42, but which when the beam 62 deflects toward the photoelectric cell 42 or the photoelectric cell 4|, respectively. The regulator 21 is arranged to supply auxiliary current of a different frequency from the source 25 or to supply direct current, more conveniently the latter.

The current responsive device23 may be an indicating instrument, a recording instrument, or any other desired type of instrument for producing a response to variations in output current of the regulator 21 in response to variations in power of the load 25 and may be placed at .a distance, if desired, for the purpose of, providing remote indications or records. The output conductors M of the current regulator 21 are connected in series with the current responsivedevice 28 across the thermocouple heating resistor |3, and preferably a choke coil 6| .is included in series with the connection in order ing current disturbances reacting upon the regulator 21, I

To prevent direct current from the auxiliary increases or decreases 39 and MI maybe connected I5 and I8 respectively and varii 86 and filmay be connected in,

series with the condensers 39 and for over- 1 coming the phase shift which would be introduced by the condensers 39 and I; 1 1 The current regulator 21a may be similar in nature to that represented at 2.'|,,and the current regulating system associated with the devicey2'|,a

includes a pair of photo electric cells Ma and 42a, cooperating with a deflecting light beam 82a,

controlled by a current responsrveinstrumentZila.

For passing the second auxiliary heating cur-,

rent through both thermocouple heaters |3 and M, the output; conductorsl l'a of the current regulator 21a are connected .to the terminals I6 and ll of the bridge 26, preferably in series with choke coils5| and 6|a.

For providing a standard :of comparison, of

temperature at which the thermocouple heaters |3 and M are kept constant, a source of conrstant voltage 94v is provided across which is connected a potentiometerilihaving an adjustable The fixed endof potentiometer 951is connected by means of a conductor 98 to one of the common terminals of. the thermocouples 2| tap 96.

and 22, and the movable tap SG-is connectedby. a conductor 91 in series with the current respon-- 1" sive device 23a to the other "of-the output 'terminals of the thermocouple 22. The thermocouples 2| and 22, and the voltage source 94 have points of like polarity connected together so that they are in parallel. The optentiometer tap 96 is set at the voltage produced by the thermocouples 2i and 22 at the temperature at which they are to be held constant by the current regulator 21a.

The current regulating system including the photoelectric follow-up arrangement 27a is such that the output current through the conductors 74a, which are connected in series with the diagonal bridge terminals l6 and H, remains constant when the light beam 62a is in a neutral position between the photoelectric light cells Md and 42a, representing no current through the current responsive device 2311. The connections of the device 21a are such that the output current increases when the beam 32a is deflected in the direction to increase the illumination of photoelectric cell Ma, and the output current decreases when the beam 62 is deflected to increase the illumination of the photoelectric cell 52a.

The following action takes place when current is drawn by the load from the line 24. The potential transformer 29 and the amplifier 33' cause a current to flow through the conductors l8 and the points 19 and 20 proportional to the line voltage. The current transformer and the amplifier 33 cause a current proportional to that of the load 25 to be applied through the conductors l5 and the points it and 57. The same phase relationship is maintained between the currents in conductors l5 and it as between the current and the voltage in the load 25.

The product of the instantaneous currents in conductors l5 and i8 represents the output of the measured electrical source 2 1 or the power supplied to the load 25; For the sake of convenience arrows have been provided representing the directions of current flow in the bridge 26 at some given instant; the solid line arrows representing the current supplied by conductors i5 and the dotted line arrows representing the current supplied by the conductors l8. It will be seen that the currents are additive in the thermocouple heater i l but subtractive in the thermocouple heater it.

Disregarding for the present the current regulators 2i and Ella, if one assumes that the heating of the thermocouples 2i and 22 is proportional to the squares of the currents flowing in the heaters and ductors i5 and it by letters a and b respectively, the output of the thermocouple 22 will be proportional to (a+b) and the output of the thermocouple 21 will be proportional to (a-b) The response of the galvanometer 23 is then proportional to (a-f-b) (ztb) which equals flab. It is seen, therefore, that the deflection of the galvanometer 23 represents the product of the two quantities a and b. However, due to heat and other causes the outputs of thermocouples and other thermal-currentresponsive devices are not strictly proportional to the square of the currents flowing therein and, therefore, if the thermocouples 2i and 22 are not accurately matched at all points of their characteristic curves and do not follow the same law of operation inaccuracies would result without the use of the regulators 2'1 and 2111.

Still disregarding the effect of the current regulator 21a, the action of the regulator 21 in equalizing the thermocouple temperatures may next be considered. It has been assumed that the direction of power flow is such that the thermocouple I3 tends to be the colder thermocouple. Accordingly, the output of the thermocouple l3 will be smaller than the output of the thermocouple i4 and the light beam 62 will be deflected to the left causing the light beam to be divided unevenly between the photoelectric cells ll and Q2. Thus the photoelectric cell 4| is caused to carry a greater current by reason of the characteristics of such photoelectric cells and the mechanism (not shown) in the followup arrangement 2?! brings about an increase of the output current through the conductors 74. When the temperature of the heater it has been raised suiiiciently to equalize the heating of the thermocouples 2i and 22, the light beam 52 falls back to the neutral position at which current output of the follow-up arrangement 2'! is maintained at the point attained.

Instead of measuring the difference in tem perature between the thermocouples 2i and 22 to determine the power of the measured circuits one measures the auxiliary heating current required to maintain the thermocouples at the same temperature, and it becomes unnecessary for the thermocouples to follow the theoretical square law. It will be understood that the instrument 28 is calibrated in terms of the R. M. S. value of power.

When the effect of the current regulator 2lla is considered it will be seen that it is also unnecessary for the thermocouples 2i and 22 to be matched or to follow the same law of relationship between output and heater current. If the power being measured is such that the thermocouple 22 would not be at the temperature corre sponding to the voltage of the potentiometer tap 95 without auxiliary current, a potential difference will take place across the current responsive device 23a setting the regulator 21in in operation to supply an auxiliary current of such value as to raise both thermocouples to the standard temperature. The fact that the thermocouples follow difierent laws of operation, i. e. do not have the same outputs at all values of heater current is without consequence because comparisons are made only at the standard temperatures at which the thermocouples are matched or have a fixed relationship between their characteristics. However, I prefer to utilize thermocouples which are accurately matched at some temperature, preferably the one corresponding to maximum current in the thermocouple M, and preferably the standard operating temperature of the thermocouples fixed by the setting of the potentiom eter 95 is the one at which the thermocouples are matched. In the arrangement shown, the arms H and it of the bridge 26 include resistors 33 and t9, condensers iii and ill, and inductances l2 and respectively, preferably tuned substantially to balance the bridge 26 at the frequency principally to be employed. The con densers it and H serve to confine the auxiliary direct current from the follow-up arrangement 2? to only one thermocouple heater l3, and to keep the bridge symmetrical both internally and with respect to the amplifiers 33 and 33.

The circuits of the stabilized amplifiers 33 and 33' are shown more in detail in Fig. 1. The amplifier circuit shown is a conventional amplifier circuit including a five-element tube 71 in the first stage and a three-element tube 78 in the final stage, with the exception that a degenerative or internal negative feed-back action is provided. The stabilizing effect is obtained by purposely designing the amplifier with excess amplification 7s and the feeding back suflicient of the output voltage to the input side in such a manner astoreduce the overall amplification to the desired amount. The feed-back feature is provided by a conductor 19 connected to the anode side of the tube 18 through a coupling condenser and connected to the control electrode circuit of the tube 11 through aresistor 81. 'In order to adjust the degree of degeneration, the resistor 8| may be provided with an adjustable tap 82, and the arrangement is such that the anode current of the tube 11 flows through the portion 83 of the resistor 8| below the tap 82. It will be seen that as the output of the amplifier 33 increases, greater voltage will be fed back to the resistor 83 increasing the potential of the tap 82, thereby decreasing the control electrode potential of the tube TI. In case of'any phase shift within the amplifier, the out-of-phase component fed back through the conductor 19 will be amplified to produce a component in the output voltage which brings it in phase with the input voltage; a

My invention is not limited to specific numerical relationships but I have obtained satisfactory results by utilizing amplifiers which would have an excess gain of about 300 times if used as straight amplifiers, about two-thirds of the excess gain being lost by reason of the degeneration produced by the presence of the resistor 83 in the anode circuit of the first tube, and the remainder being cut to about one-hundredthby the direct feed-back 19. The direct feed-back also reduces the effects of any changes in the amplifier such as phase shift or amplification variations, etc. about of .what they would be without the feed-back. Thus with a direct feed-back of 100, a 10% change in the amplifier would a /10% error in the output. In order that the amplifiers 33 and 33 may be alike, the input transformers 29 and 30 may be designed with ratios such as to give the same voltage output for full-scalevoltage and current of the measured circuit 24.

In order to avoid disturbance from stray fields or other interference, the input transformers 29 and 30 may be made astatic by providing two sets of windings 86 and 81 which are reversed in their relative physical positions. Input condensers 88 and 89 may likewise be provided in the case of high frequency measurements. in order to prevent excess voltage drops in the input transformer primaries by resonating them to the appr'oximatefreq'uency of the measured circuit.

In accordance with the provisions of the patent statutes, I have described the principle of operation of my invention together with the apparatorepresent the best tus which now consider embodiment thereof but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. Apparatus responsive to the product of two currents comprising a bridge including four arms connected together to form a square, terminals two opposite points of said square to serve as connections for one of said currents, and a second pair of terminals at the two remaining opposite points of the square to serve as connections for the other of said currents, two adjacent arms of said bridge comprising thermocouple heaters,

produce only current supplied by the thermocouples associated with said thermocouple heaters, a current responsive device to which said thermocouples are connected in opposition, an adjustable source for supplying auxiliary current to one of said thermocouple heaters, control mechanism in operative relation with the current responsive device for keeping the adjustable source in the adjustment producing a current at which the thermocouple temperatures are balanced and no current flows in the current responsive device, a second adjustable source for supplying a second auxiliary current to both of said thermocouple heaters, a standard voltage source, a second current responsive-device connecting said standard voltage across said'thermocouples, and control mechanism in operative relation to the second .current responsive device to maintain the second auxiliary current at the value holding the thermocouples at the temperature at which their voltage balances the standard voltage.

2. Apparatus responsive to the product of two currents comprising a bridge including four arms connected together to form a square, terminals at two opposite points of said square to serve as connections for one of said currents, and a second pair of terminals at the two remaining opposite points of the square to serve as connections for the other of said currents, two adjacent arms of said bridge comprising thermal current responsive devices, means for supplying auxiliary current to one of said thermal current responsive devices, means responsive to the relative current effects in the two thermal current responsive devices for controlling the auxiliary current and maintaining a predetermined relationship between the temperatures of the two thermal current responsive devices, means for supplying a second auxiliary current to both of said thermal current responsive devices and means responsive to fluctuations in temperatures in one of said thermal current responsive devices for controlling the second auxiliary current to maintain said thermal current responsive device at a predetermined temperature.

3. Apparatus responsive to the product of two currents comprising a bridge including four arms connected together to form a square, terminals at two opposite points of said square to serve as connections for one of said currents, a second pair of terminals at the two remaining opposite points of the square to serve as connections for the other of said currents, means responsive to the relative values of resultant efiects of current flowing in two adjacent arms of the said bridge,

an adjustable auxiliary current source connected bridge arms, means in operathe current source and current effects in the to one of said latter tive relationship between the means responsive to said adjacent bridge arms, for maintaining the auxiliary current at a value giving a predetermined relationship between the resultant current effects in the said last mentioned two adjacent bridge arms, a second adjustable source of auxiliary current connected to both of said last mentioned bridge arms in series, and means responsive to the resultant current effects in one of said last mentioned bridge arms for adjusting the second auxiliary source to maintain the resultant in the last mentioned bridge HARRIS arm.

A. THOIVIPSON.

current effects constant 

